1. Field of the Invention
The present invention relates to a liquid crystal display device, and more particularly to a liquid crystal display device using an optically compensated bend (OCB) alignment technique which can realize a wide viewing angle and a high response speed.
2. Description of the Related Art
Liquid crystal display devices have been applied to various fields by taking advantage of their features such as light weight, small thickness and low power consumption.
In recent years, attention has been paid to a liquid crystal display device, to which the OCB mode is applied, as a liquid crystal display device which can improve the viewing angle and response speed. The OCB mode liquid crystal display device is configured such that a liquid crystal layer including liquid crystal molecules, which are bend-aligned in a state in which a predetermined voltage is applied, is held between a pair of substrates. Compared to a twisted nematic (TN) mode, the OCB mode is advantageous in that the response speed can be increased and the viewing angle can be increased since the effect of birefringence of light, which passes through the liquid crystal layer, can optically be self-compensated by the alignment state of liquid crystal molecules.
There has been proposed an optical compensation sheet including hybrid-aligned discotic liquid crystal molecules, as an optical sheet for further improving the viewing angle characteristics in the liquid crystal display device to which the OCB mode is applied (see, e.g. U.S. Pat. No. 3,118,197).
In the above-described OCB mode liquid crystal display device, there is a problem that the hue varies depending on the direction in which the screen is viewed. Specifically, in the state in which a black image is displayed by applying a predetermined voltage to the liquid crystal layer, if the viewing angle is gradually increased from the normal direction of the screen along a direction perpendicular to the rubbing direction of the alignment film, a black image is colored. At this time, for example, if the rubbing direction is a vertical direction of the screen, the hue is different between the case of increasing the viewing angle from the normal direction toward the right side of the screen and the case of increasing the viewing angle from the normal direction toward the left side. For example, the black image becomes reddish on the right side of the screen, and the black image becomes bluish on the left side of the screen.